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Barrel Efficiency, Tech Tip #1

Guys,

I have decided to do a tech tips series of posts so you will understand certain technical processes that go on in the paintball gun. We have tested everything I will talk about and any speculations will be pointed out.

In the tech forum there is a long post on what is the most efficient barrel so here are the facts.

Barrel Efficiency, Tech Tip #1

Barrels are only there to accelerate the ball from a standstill to 300 fps. In theory they also help with accuracy but that's another post. The ball goes through incredible acceleration on its way down the barrel. The balls acceleration rate is approx. 50,000 feet per second to get to 300 feet per second in 10 inches. The entire barrel travel time is about 6 thousandths of a second and this means the ball is seeing about 1500 G's when its getting pushed out the gun. Although this may sound incredible if someone out there would like to do the math you will see that I'm close.

Air pressure behind the ball is what causes this acceleration to happen. This pressure varies between the different guns but is generally between 50 to 125 pounds per square inch at its peak. The air pressure peaks right when the ball starts moving down the barrel, after that, the ball moving down the barrel creates a bigger chamber so the pressure drops. This is why low pressure guns are a myth, in reality all guns shoot at considerably lower pressure than 200 psi.

Peak pressures above 150 psi tends to break balls down the barrel due to really high acceleration and G forces. If you don't have any way to control the peak pressure behind the ball, the only way you can change it is to go with lower pressure in the air chamber, hence low pressure guns. AGD uses the precise contour of the power tube tip to release air in a controlled manner behind the ball to limit peak pressures to around 60-80 psi..

It is simple to understand that the harder you push something the faster it will accelerate and get up to speed in a shorter distance. So what distance do we have to get the ball up to speed? The effective length of the barrel is from the balls position before it's fired, to the place in the barrel where the pressure gets released, This is usually at the first porting holes or the step in the barrel. Porting is there to release gas pressure!! You are effectively stopping the acceleration at the ports so your 14" barrel that is half full of holes only has an effective length of 7".

Now we understand that we need to limit the peak pressure behind the ball to keep it from blowing up, and that the pressure drops as the ball moves down the barrel. The next question we need to ask is, how far down the barrel does the ball have to go before the pressure gets to low to do anything useful? That answer is 8-10 inches. We know this from looking at the graphs that our gun dyno puts out. If your peak pressure is higher, say over 100 psi you can get away with a shorter barrel, if it's lower then you need a longer barrel. Since AGD is the only gun manufacturer to actually test their pressures behind the ball you might have a hard time getting this info for other guns.

So as far as our guns are concerned, the best efficiency would be had with an 8-10" effective length barrel. Since two piece ported barrels with an effective length of about 5-6" are the rage right now you hear a lot of complaints about gas efficiency. Under some circumstances there is a good reason to use a short effective length barrel. Short barrels cut off the acceleration abruptly by venting and this has the effect of tightening up the shot to shot velocity variation. If you need this at the expense of efficiency then go ahead. Tighter velocity control usually translates into some improvement in accuracy due to better consistency.

So if you want the best of all worlds, limit your peak pressure, let your ball accelerate all it wants, don't follow the crowd and keep asking questions.

Gee, I've been telling people that before... Not with the exact numbers, though. Plus I am no rocket scientist. 12in Lapco Bigshot-"effective" length of around 10 inches. I don't have mine here to measure, but the only porting on the thing is in a band right before the muzzle break.

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"Don't spend so much on parts that you can't afford to play."

For those of you who don't understand a Barrel that has more effective barrel length is more gas effecient. Effective barrel length is the portion of the barrel that is unported. However barrels with less effective barrel length and more porting give you tighter shot grouping(more accuaracy). I know Tom explained it well but I didn't understand at first I thought I might as well simplify it further.

<font face="Verdana, Helvetica, sans-serif" size="2">Originally posted by AGD:Barrels are only there to accelerate the ball from a standstill to 300 fps. In theory they also help with accuracy but that's another post.</font>

What about bore sizing? Is it as substantial an issue as it's been made to be lately, or is it not so important (ref. the Palmer theory of the paintball distorting under the initial impact of the airburst so that all sides are in contact with the barrel breech when acceleration begins)?

The Dye 12" one piece has 7" of unported length. Shouldn't I measure the length from the beginning of the paintball? It would be less then. I was thinking of putting tape around the gun end of the porting covering about an inch so wouldn't that in effect make the barrel more efficient?

The 2 piece dynamics confuses me a little. As the paintball goes to the 2nd step. Doesn't the ball continue to accelerate until it hits the porting? I think the acceleration should still continue but at a lower acceleration because the bore is larger. I gotta try some experiments this weekend with a boomstick. I heard 8-12 was the ideal unported barrel length.

Why doesn't AGD make some good barrels as an optional buy? They seem the most serious about paintball dynamics. My stock barrel shoots decent but it doesn't have a mirror finish interior which gives less friction.

This is exactly why I've played with a mag for over ten years. AGD never talks any smack about other manufacturers but if you ask the right question they will give you the answer and back it up with real science and data. From there they let us make a decision based on fact not hype.

Open up those archives and show the world some real data although the 2inch folder on mag bumpers could probably be left in the draw...

I would really like to have that film of the ball being shot through a glass barrel available for all. The close up of the ball in the breech and the ball exiting through the smoke trail (I know there's a bit on the RT video). As well as the ball in flight, that stuff is amazing to watch.

I also think some barrel testing with and without ports and some sort of trace element in the gas to actually see if it does exit the ports behind the ball as it goes past would be very interesting!

How about a new breed of two piece glass barrels lol... gotta keep up with fashion

Firewall,
Porting is there to release gas pressure and to quiet the sound. An unported barrel is very loud when you fire a paintball through it.
So it's like a tradeoff:
Unported = loud but more gas efficient
Ported = quieter but less gas efficient

Man, I hate to do this: I believe you have the acceleration rates wrong. They are a bit overstated. The rate to push the ball is not 50,000 fps. That is about the escape velocity to achieve earth orbit. To hit that number in 10 inches would push the g-forces to over 22,000, enough to permanetly compress titanium. If you are talking about the initial acceleration from zero to any number, that is proportionally the highest attainable acceleration number on the curve, and mathmatically approaches infinity. Also, if you did go to 50,000 fps, you have to decelerate the ball down to the 300 fps mark and therefore put the paintball through double the stress. Am I off-base here, or did I miss something? Brent Jackson, Pink Fluffy Ballerinas.